Mao, Huahai

Abstract [en]

Alumino-silicate systems are of great interest for materials scientists and geochemists. Thermodynamic knowledge of these systems is useful in steel and ceramic industries, and for understanding geochemical processes. A popular and efficient approach used to obtain a self-consistent thermodynamic dataset is called CALPHAD. It couples phase diagram information and thermochemical data with the assistance of computer models. The CALPHAD approach is applied in this thesis to the thermodynamic modelling and assessments of the CaO-Al2O3-SiO2, MgO-Al2O3-SiO2 and Y2O3-Al2O3-SiO2 systems and their subsystems. The compound energy formalism is used for all the solution phases including mullite, YAM, spinel and halite. In particular, the ionic two sub-lattice model is applied to the liquid solution phase. Based both on recent experimental investigations and theoretical studies, a new species, AlO2-1, is introduced to model liquid Al2O3. Thus, the liquid model corresponding for a ternary Al2O3-SiO2-M2Om system has the formula (Al+3,M+m)P (AlO2-1,O-2, SiO4-4,SiO20)Q, where M+m stands for Ca+2, Mg+2 or Y+3. This model overcomes the long-existing difficulty of suppressing the liquid miscibility gap in the ternary systems originating from the Al2O3-free side during the assessments. All the available and updated experimental information in these systems are critically evaluated and finally a self-consistent thermodynamic dataset is achieved. The database can be used along with software for Gibbs energy minimization to calculate any type of phase diagram and all thermodynamic properties. Various phase diagrams, isothermal and isoplethal sections, and thermochemical properties are presented and compared with the experimental data. Model calculated site fractions of species are also discussed. All optimization processes and calculations are performed using the Thermo-Calc software package.

Abstract [en]

The AI(2)O(3)-SiO2 system has been reassessed using a solution model for mullite extending from sillimanite to a hypothetical state of alumina. The property of sillimanite, to be used to describe one of the end-members, was extracted from an analysis of the T-P phase diagram for AI(2)SiO(5) polymorphs. It was possible to represent the information on the range of stability of mullite, including some showing that mullite extends to higher SiO2 contents than represented by the composition of 3:2 mullite. An attempt was made to model the liquid with the ionic two-sublattice model using a new species AIO(2)(-1). The pressure dependence of AI(2)SiO(5) polymorphs was optimized by a new model recently implemented in Thermo-Cale.

Sundman, Bo

Abstract [en]

The thermodynamic properties of the liquid phases in the CaO-Al2O3 and MgO-Al2O3 systems are reassessed in order to provide an adequate basis for fitting information on the ternary CaO-Al2O3-SiO2 and MgO-AI(2)O(3)-SiO2 systems, especially the miscibility gap. The modelling of Al2O3 in the liquid phase is modified from the traditional formulae with the liquid phase now described by the ionic two-sublattice model as (Al+3, Ca+2)p(AlO2-1, O-2)(Q) and (Al+3, Mg+2)(P)(AlO2-1, O-2)(Q), respectively.

Abstract [en]

The CaO-Al2O3-SiO2 system has been assessed with the CALP-HAD technique, based on recent assessments of its binary systems. A new species AlO2-1 was introduced for modeling liquid Al2O3. The ternary liquid phase was described using the ionic two-sublattice model as (Al+3, Ca+2)(p) (AlO2-1, O-2, SiO4-4 SiO20)(Q). The available experimental data were critically examined and a self-consistent set of thermodynamic descriptions was obtained. Various phase diagrams and property diagrams, including isothermal sections, isoactivity lines, and a projection of the liquidus surface, are presented. Information on viscosity seems to support the use of the AlO2-1 species.

Abstract [en]

Thermodynamic properties of the phases in the MgO-Al2O3-SiO2 system were assessed, resulting in a set of self-consistent thermodynamic data. The two ternary Compounds, cordierite and sapphirine, were optimized from subsolidus reactions. The liquid phase was described by the ionic two-sublattice model with a new species AlO2-1 yielding the formula (Al+3,Mg+2)(p)(AlO2-1 O-2,SiO4-4,SiO2o)(Q). Projection of the liquidus surface was calculated. Various isothermal and isoplethal sections were compared with the experimental data.

Fabrichnaya, Olga

Abstract [en]

Phase equilibria and thermodynamic properties at I bar in the Y2O3-Al2O3-SiO2 ternary system and its constituent binaries Y2O3-Al2O3 and Y2O3-SiO2 have been reevaluated using the CALPHAD approach. The liquid phase is described by the ionic two-sublattice model with the formula (Al+3, Y+3)(p)(AlO2-1, O-2, SiO4-4, SiO4-4, SiO20)(Q). The SiO2 solubility in the YAM phase was described using a Compound energy model. Two clatasets of self-consistent model parameters are presented. However, the rather meagre and scattered experimental data imply that the present assessments should be regarded as provisional. Some critical experiments are suggested for this system.